Domains, DNS & Business Email

Changing mail providers changes the systems authorized to send messages. Old SPF entries, missing DKIM keys, or a DMARC policy that expects the previous provider can cause messages to fail authentication even when users can send mail. What to check Identify all outbound senders, inspect message headers, and compare SPF, DKIM selector, and DMARC...

Changing an outbound mail IP can affect reverse DNS, SPF authorization, provider reputation, and recipient allowlists. Messages may be accepted by some domains and rejected by others. What to check Confirm the actual sending IP from message headers and compare PTR, forward DNS, SPF, DKIM, DMARC alignment, and rejection text. Check whether applications...

A mobile carrier or device may use different DNS, IPv6, proxy, or content filtering behavior than a home or office network. One network succeeding does not prove the domain resolves and serves correctly for all visitors. What to check Compare A and AAAA resolution, certificate and redirect behavior, proxy or CDN response, and network path across...

Outbound mail can work while inbound delivery fails if MX records are missing, point to the wrong host, or have not propagated. Some providers also require mailbox creation or domain verification before accepting messages. What to check Check authoritative MX and related host records, domain verification, mailbox existence, inbound gateway logs, and...

Web and mail services can use different DNS records and providers. A site may load correctly while MX, SPF, DKIM, or DMARC records are missing, duplicated, or published in a zone that is not authoritative. What to check Query authoritative nameservers for mail records, confirm the exact hostname and TXT values, and compare with the active mail...

A renewal should preserve DNS, but expired nameservers, registrar lock changes, account ownership issues, or a missed DNS hosting renewal can interrupt mail even if the domain registration is current again. What to check Check registrar status, active nameserver delegation, authoritative MX records, DNS provider account, mail host availability, and...

A site can work over IPv4 while failing over IPv6 if an AAAA record points to the wrong host, the web server is not listening on IPv6, or firewall and certificate settings differ. Some visitors prefer IPv6 automatically. What to check Compare A and AAAA answers, test each route, inspect IPv6 firewall and listener configuration, and verify the hostname...

Email access can vary between Wi-Fi and mobile data because of VPN routing, DNS, firewall policy, carrier filtering, or mail app account configuration. The mailbox itself may be available while one network path is blocked. What to check Compare incoming and outgoing server names, ports and encryption, DNS answers, VPN state, carrier network behavior,...